[CentOS] gigE -> 100Mb problems

I've got a pair of identical CentOS 6.7 servers, with SuperMicro X8DTE-F motherboards, these have 2 each Intel 82574L ethernet ports. The eth0 ports are plugged in with 10' runs of brand new cat 5e cable to a Cisco Nexxus 9000 switch (provided by the data center).

These servers keep coming up at 100baseT rather than gigE. I've swapped ports and cables with a different server, that server gets gigE but these supermicro's are stuck at 100baseT regardless of the port or cableused.

'ethtool eth0' says its gigE, but 'mii-tool -v eth0' says its 100baseT and doesn't even list gigE as an option, and the cisco switches see it as 100baseT too.

anyone else run into anything like this before?